Iodous acid - a more efficient nucleation precursor than iodic acid.

Iodous acid (HIO 2 ), a vital iodine oxyacid, potentially plays an important role in the formation of new particles in marine areas (He et al. , Science , 2021, 371 , 589-595). However, the nucleation mechanism of HIO 2 is still poorly understood. Herein, the self-nucleation of HIO 2 under different atmospheric conditions is investigated by a combination of quantum chemical calculations and the Atmospheric Cluster Dynamics Code (ACDC) simulations. The results indicate that HIO 2 can form relatively stable molecular clusters through hydrogen bonds and halogen bonds, and the self-nucleation of HIO 2 proceeds by sequential addition of HIO 2 or HIO 2 -based small clusters. Besides, in order to better illustrate the role of HIO 2 in new particle formation (NPF) in marine areas, we compare its nucleation properties with those of iodic acid (HIO 3 ), a significant iodine-containing nucleation precursor in marine regions. We find that the cluster formation rate of the self-nucleation of HIO 2 is higher than that of the self-nucleation of HIO 3 although [HIO 2 ] is lower than [HIO 3 ], which indicates that the HIO 2 molecule is a more efficient nucleation precursor than the HIO 3 molecule. Therefore, the self-nucleation of HIO 2 could become one of the most important sources for NPF in marine areas, which could provide potential theoretical evidence for explaining the intensive NPF events observed in these areas.